The present invention relates in general to a storage apparatus system for carrying out the copy (the remote copy) of data to another storage apparatus system which is located in an out-of-the-way place. More particularly, the invention relates to an information processing system for carrying out the remote copy which is of the type in which the order of writing data from a host computer to a storage apparatus system does not match the order of transmitting data from a storage apparatus system having the data written thereto to another storage apparatus system.
In an information processing system having a host computer and a plurality of storage apparatus systems, as the technology of carrying out the copy of data between the storage apparatus systems, there is known the remote copy.
By the remote copy is meant the technology in which a plurality of storage apparatus systems which are located physically apart from one another carry out the copy of the data, i.e., the double writing of the data between the storage apparatus systems without interposition of the host computer.
The storage apparatus system is a system including a plurality of storage apparatuses and a controller for controlling these storage apparatuses.
In the information processing system which carries out the remote copy, the storage apparatus systems which are respectively arranged in the places physically remote from one another are electrically connected to one another through dedicated lines or public lines. Of logical storage areas (hereinafter, referred to as xe2x80x9clogical volumesxe2x80x9d, when applicable) which a certain storage apparatus system has, the logical volume having the same capacity as that of the logical volume subjected to the remote copy (hereinafter, referred to as xe2x80x9cthe source volumexe2x80x9d for short, when applicable) is ensured in the storage apparatus system to which the logical volume as the source of the copy is copied. This ensured logical volume (hereinafter, referred to as xe2x80x9cthe destination volumexe2x80x9d, when applicable) is formed in such a way as to show one-to-one correspondence relation with the logical volume as the source of the copy.
The data of the logical volume as the source of the copy is copied to the logical volume as the destination of the copy through the associated one of the dedicated lines or public lines.
When the data contained in the logical volume as the source of the copy is updated, the updated data is transferred to the storage apparatus system having the logical volume as the destination of the copy through the associated one of the dedicated lines or the like and the updated data is also written to the logical volume as the destination of the copy corresponding to the logical volume as the source of the copy.
If the technique of the remote copy is employed, then in the information processing system having a plurality of storage apparatus systems, the logical volume of the same contents can be held in a plurality of storage apparatus systems.
The technique relating to the remote Copy is disclosed in U.S. Pat. No. 5,742,792. In U.S. Pat. No. 5,142,792, the technique called the adaptive copy is further disclosed.
By the adaptive copy is meant one of the remote copy techniques. The adaptive copy is the remote copy method wherein before the data written from the host computer to the local storage device is copied to the remote storage device, the information exhibiting the completion of write is returned back to the host computer.
In the adaptive copy, the transmission order of data is not serialized, and hence the order of writing the data to the logical volume as the source of the copy by the host computer may be different from the order of transferring these data to the logical volume as the destination of the copy in some cases (hereinafter, such remote copy is referred to as the remote copy of xe2x80x9cno guarantee to orderxe2x80x9d, when applicable).
When the host computer writes repeatedly data to the same location in the destination volume on the basis of that property, only the data which has been written thereto lastly can be transmitted to the storage apparatus system having the logical volume as the destination of the copy. Therefore, the load on the network such as the dedicated line between the storage apparatus systems can be reduced.
On the other hand, when the host computer in which the file system used in the so-called open system is incorporated writes the data to the storage apparatus system, in general, the buffer and the like provided in the host computer, whereby an instruction to transfer the data from an application program to the file system is made asynchronously with the operation of writing the data to the storage apparatus system.
But, in the case that the data in the file is destroyed due to various problems, in order to keep the coherency of the file system structure, with respect to at least the directory and the meta-data such as i-node which are used to manage the file system, the operation of issuing an instruction to transfer the data, i.e., the directory and the meta-data from the host computer to the storage apparatus system is carried out synchronously with issuing of the write command from the application program running on the host computer to the file system. The above-mentioned technique is disclosed in an article of xe2x80x9cThe Design and Implementation of a Log-Structured File Systemxe2x80x9d, Mendel Resenblum and John K. Ousterhout, ACM Transactions on Computer Systems, Vol. 10, No. 1, February 1992, page 29.
By executing such a processing, even if the data in the file which is buffered in the host computer is lost due to the asynchronous writing by an abrupt power source shutdown or the like, the meta-data is not lost at all. So, the coherency of the file system structure is kept and the damage can be kept to a minimum even though the data itself is lost.
The remote copy of no guarantee to order is carried out, whereby the load which is applied to the network of the dedicated line or the like distributed between the storage apparatus systems can be reduced. However, in the remote copy of the order no guarantee based on the prior art, it is not taken into consideration up to the coherency of the meta-data in the destination volume to keep the coherency of the file system structure, and hence there is the danger that a large amount of files would be lost.
More specifically, in the case where the data which has been written to the logical volume as the source of the copy by the file system is not transferred to the logical volume as the destination of the copy synchronously with the operation of writing the data to the file system, with respect to the directory structure of the storage apparatus system having the logical volume as the destination of the copy, the file system of the host computer may not become the-state which is intended in some cases.
Under above circumstance, the data of the storage apparatus system having the logical volume as the source of the copy is destroyed, even if the file system recovery program such as fsck runs for the storage apparatus system having the logical volume as the destination of the copy, it does not function effectively, and as a result the possibility that many files are lost is high. Because, the fsck with on the basis of the assumption that there is no contradiction between the directory structure of the storage apparatus system having the source volume and the directory structure of the storage apparatus system having the destination volume.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide means for even when carrying out the remote copy of the no guarantee to order, keeping the coherency of the file system structure in the destination volume, so that even when the data in the source volume is destroyed, the data in the source volume is recovered from the destination volume by maintaining the coherency of the source volume.
In order to attain the above-mentioned object, according to the present invention, there is provided a storage apparatus system having a host computer, a main storage apparatus system and a substorage apparatus system which is electrically connected to the main storage apparatus system, wherein an instruction is transmitted from the host computer to the main storage apparatus system in such a way as to maintain the data of the main storage apparatus system at a time point when the instruction is issued and the fixed data is copied to the substorage apparatus system.
In addition, the storage apparatus system may also be configured in such a way that the data which is maintained in the main storage apparatus system is transferred to the substorage system, and after completion of the transfer of the maintained data, a signal exhibiting the completion of the transfer of the data is transferred from the main storage apparatus system to the sub-storage apparatus system, go that with the reception of the signal exhibiting the completion of the data transfer as a turning point, the data is structured in the substorage apparatus system.
In addition, the step of maintaining the state of the data is to store the data in a first storage area of the main storage apparatus system until the instruction is issued from the host computer to copy, after the instruction has been issued from the host computer, the data which was stored in the first storage area at a time point of the issue of the instruction to a second storage area of the main storage apparatus, and in the step of transferring the data, the data which has been copied to the second storage area can also be transferred to the sub-storage apparatus system.
In addition, in the step of structuring the data, the maintained data which has been transferred is stored in a third storage area of the substorage apparatus system so that using the data which is held in the third storage area, the maintained data can also be structured in a fourth storage area of the substorage apparatus system.
Also, according to the present invention, there is provided a storage apparatus system including: a main storage apparatus system which has a first storage area, a second storage area and a main disk controller and which is electrically connected to a host computer; and a substorage apparatus system which has a third storage area, a fourth storage area and a sub-disk controller and which is electrically connected to the main storage apparatus system, wherein the main disk controller includes: means for recording data which has been sent from the host computer in the first storage area until an instruction is issued from the host computer; means for in response to the instruction issued from the host computer, copying the data which is recorded in the first storage area to the second storage area; and means for sending the copied data to the substorage apparatus system. Then, the sub-disk controller includes; means for receiving the data sent thereto to hold the received data in the third storage area, and means for structuring the data, which is held in the first storage area at a time point when the instruction has been issued from the host computer, in the fourth storage area using the data which is held in the third storage area.
According to another aspect of the present invention, the host computer issues a freezing instruction to the storage apparatus system as the destination of the data transfer, and the storage apparatus system as the source of the data transfer transfers the data, which is held in the storage apparatus system at a time point of the issue of the freezing instruction, and the arrangement thereof (hereinafter, referred to as xe2x80x9cthe volume imagexe2x80x9d for short, when applicable) to the storage apparatus system as the destination of the data transfer. All data transfer completion is reported which means that the volume image at a time point when the freezing instruction has been issued has already been transferred to the storage apparatus system as the destination of the data transfer.
In the storage apparatus system as the destination of the data transfer, the data of the volume image, at a time point of the issue of the freezing instruction, in the source of the data transfer is held, and when the report exhibiting the completion of the data transfer will be made next time, the volume image will be updated using the transferred data.
As a result, when the disk unit system in the source of the data transfer at an arbitrary time point has become unusable, it is possible to utilize the volume image which is held in the storage apparatus system as the destination of the data transfer.